Late Pleistocene (MIS2) environmental changes and palaeoclimatic dynamics around Aiding Lake in the Turpan Basin, Xinjiang Province, NW-China

A 12 m sediment core from the Aiding Lake basin in the today hyper-arid Turpan depression (Autonomous Xinjiang Province, NW-China) has been studied. The core, which was drilled near the deepest point of the endorheic Turpan basin (154 m below sea level), revealed several climatic and palaeoenvironmental changes during the Late Pleistocene. The sediments which were analyzed relating to sedimentology (grain size), geochemistry (Ti/Al ratio, chemical index of weathering, total organic and inorganic carbon, sulfur, nitrogen), and magnetic susceptibility, are of fluvial, eolian, and lacustrine origin. Age control was done by five C-14 dates. Reservoir effects for the stratigraphic units were considered. Less saline conditions lasted until the end of the Pleistocene, forced by stronger westerlieS and low, but increasing temperatures. Sometime after Dansgaard-Oeschger event 1 (14.6 ka) up to present, environmental conditions were arid and Aiding became a salt lake. High sand contents indicate eolian input during a period of cold, windy and arid conditions, associated with Heinrich event 2 (-24.8-23.4 ka cal BP; HEMMING 2004), whereas high sand input of the uppermost 2 m and salt accumulation reflects a general change to drier conditions since the Pleistocene/Holocene transition. In summary, the Lake decreased from its maximum size of around 3000 km(2) during the MIS3 to a seasonal small lake today. The measured Rb/Sr ratio, generally used as an indicator for weathering conditions of lake catchments, with reduced Sr influx during arid periods due to weak chemical weathering, has to be interpreted differently for Aiding Lake: Very low Rb/Sr ratios in the uppermost 2.7m similar to that of unweathered loess represent the recent drought and Sr accumulation during the Holocene. Contrary to other studies, we found e.g. that Rb/Sr dynamics do not indicate the intensity of past chemical weathering, but allows the distinction of different source areas and the decoupling of weatherin